This invention relates to a technology for detecting interaction between substances, and more specifically to a technique for detecting interaction between substances while making use of an electrodynamic effect to eliminate adverse effects of an electrochemical reaction.
In recent years, integrated bioassay plates holding thereon predetermined DNAs microarrayed by microarray technologies and generally called “DNA chips” or “DNA microarrays” (hereinafter collectively called “DNA chips”) have been developed, and are finding utility in gene mutation analyses, SNPs (single-base polymorphisms) analyses, gene expression frequency analyses, gene network analyses, and the like. In addition, they are expected to find broad applications in drug developments, clinical diagnoses, pharmacogenomics, tailor-made remedies, research on evolution, forensic medicine, and other fields.
Sensor chip technologies represented by such DNA chips and protein chips with proteins integrated thereon quantitate the existing amounts of target substances by making use of specific interactions between detecting substances (which are often called “probes”) immobilized on solid-phase plates and the target substances.
Taking a DNA chip as an example, single-stranded DNA fragments having a segment of the DNA sequence of a target to be analyzed are immobilized beforehand. If DNA molecules having a sequence complementary to the DNA fragments exist in a sample, the DNA fragments and the DNA molecules specifically combine together (in other words, hybridize with each other) to form double-stranded DNA. Relying upon the detection of this double-stranded DNA by a fluorescence labeling technique or the like, a determination is made as to whether or not the DNA molecules have been expressed in the sample solution. Immobilization of numerous single-stranded DNA fragments of different DNA sequences makes it possible to efficiently perform an analysis as to whether or not plural kinds of DNAs have been expressed or to provide an analysis of expression of a single kind of DNA with redundancy such that the accuracy of the analysis is increased.
However, such sensor chips as described above rely upon natural interaction between biomacromolecules so that the reaction rate is determined by a reaction rate constant which is in turn determined by the step of a transport by diffusion and the interaction. Accordingly, the accuracy of the reaction is determined by the equilibrium constant of the interaction. If a sample contains not only true target molecules but also noise molecules having a similar level of affinity to a detecting substance as the true target molecules, these noise molecules are bound to some extent to the detecting substance, leading to a reduction in the accuracy of an analysis by the sensor chip.
With a view to solving this problem, several approaches have been proposed. For example, there are techniques which make use of an electrodynamic effect. Reference will hereinafter be made to related art techniques, which can be placed as constituting a general technical standard in relation to the present invention. Firstly, JP-A-2004-524823 discloses a technique for amplifying an mRNA transcript from a biological sample to obtain amplicons and electrically hybridizing the amplicons to a probe bound (immobilized) at predetermined locations of a support.
To remove molecules other than true target molecules, these former molecules having undesirably hybridized with a ligand in interaction between biomacromolecules (in this case, a hybridization reaction between DNAs), JP-A-2002-541823 proposes a method for applying a direct voltage, which has a polarity opposite to a voltage applied for the improvement of a transporting step, after the interaction between the biomacromolecules (i.e., the hybridization reaction between the DNAs).
Further, JP-A-2004-135512 proposes to improve the efficiency of hybridization by applying a high-frequency alternating-current voltage or the like to induce polarization of nucleotide chains such that they are caused to migrate (dielectrophoresis) in a non-uniform electric field.